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The technology of glass and ceramics - Hlavac J.

Hlavac J. The technology of glass and ceramics - Oxford, 1983. - 429 p.
Download (direct link): tehnologyofglass1983.djvu
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at the same time a similar material was developed in Hungary (minelbit).
The continuous production with a daily output of 1500 m2 of sheet
slagsital was initiated in the USSR in 1966. A schematic diagram of the
process is shown in Fig. 150. After melting in a tank furnace, a sheet is
formed by pouring between rollers; in a tunnel kiln crystallization is
then performed in two stages. The sheet is 3 m in width and 5 - 25 mm in
thickness.
In order to transform the basic slag into a melt capable of being
shaped, the composition has to be adjusted by additions of sand and other
components. The mixture for melting contains 50 to 65% blast-furnace
slag, 20 to 40% quartz sand, up to 12% clay, 4 to 6% Na2S04, 1 to 3%
carbon and 0.5 to 2% of a nucleating agent. The composition of the final
product lies within the following ranges: 52 to 62% Si02, 5 to 15% Al203,
22 to 28% CaO, 1 to 7% MgO, 4 to 8% Na20 -f + K20 (Bondarev, 1971).
Sulphides, e.g. such as MnS + FeS (1.5 to 5%) may be used as effective
nucleating agents, which can also be formed by reduction of sulphates
during melting. The ware is of dark colour when MnS-FeS are used; by
introducing ZnO into the charge the sulphides are converted to ZnS which
is white, so that a product of white colour can be obtained; coloured
ware is produced by the use of suitable colouring substances (CdS, CdSe,
CoO). Combinations of sulphides and fluorides, Ti02 -f P205, Cr203 MgO,
and others may likewise be used as nucleating agents.
The crystallization is carried out in two stages: at the lower
temperature the process involves metastablc separation, while at the
higher temperature (800 to 1000 C), the main phases wollastonite CaO .
Si02 or anorthite CaO . A1203 . 2 Si02 crystallize. The materials are
therefore derived from the system CaO-A1203 -Si02 (cf. Fig. 151).
According to Voldan (1972), the optimum products arise at a composition
found in the neighbourhood of the anorthite-mullite boundary line in the
direction towards the wollastonite-anorthite-Si02 ternary eutectic.
However, the materials melt at high temperatures. In the case of a higher
MgO content, diopside or pyroxenes are preferentially separated, and for
a higher content of iron oxides, hedenbergite FeO . CaO. . 2 Si02 is
crystallized.
242
The slagsital made through this technology contains 60 to 70%
crystalline grains up to 0.5 - 1 jim in size. The bending strength is in
the range of 90 to 130 MPa, a = = 65 to 85 x 10~7, the porosity being
zero. Slagsital in the form of plates finds its main application as
cladding in the building industry.
CaO 10 20 30 3Ca0.Al203 12Cq0.7AI203 CaO.Al^ CaO
2Al203 Ca0.6A;203 Al^
--------- wt %
FIG. 151. Phase diagram of the system CaO-Al203-Si02 (Rankin and Wright,
with modifications based on more recent data; from Miian and Osborn,
1965),
Other types of metallurgical slags, power station fly-ash and other
waste materials can in principle also be processed in a similar way.
Difficulties arise when the initial raw material shows variable
composition; unfavourable economic indices may be offset by the need to
dispose of troublesome wastes.
Similar materials have also found application as gravel in road
building, in particular for rough antiskid layers; white types are
suitable for the construction of light--coloured roads which ensure
better visibility at night (e.g. the Danish Synopal
243
based on wollastonite, molten from a mixture of sand and limestone). The
technology of making artificial gravel is quite different from those
dealt with above: rotary kilns are used for both melting and
crystallization.
REFERENCES Beall G. H., Glass Technol.,
19 (1978) 109
Beall G. H., Montierth M. R. and Smith G. P., Ber. DKG, 49 (1972) 119
Berezhnoy A. J., Sitals and Photositals (in Russian), Mashinostroenie,
Moscow 1966 (Бережной А. Й., Ситаллы и фотоситаллы, Машиностроение,
Москва).
Bondarev К. Т., Ргос. 9th Int. Congress Glass, Versailles, 1971, p. 1237
Corning Glass Works, Am. Ceram. Soc. Bull., 36 (1957) 279 Dusil J. and
Strnad Z" Sklar a keramik, 24 (1974) 105 Eppler R. A., J. Am. Ceram.
Soc., 45 (1963) 100
Freimann S. W. and Hench L.L. (Ed.), Advances in Nucleation and
Crystallization, Symp.
Glass Div., Am. Ceram. Soc., 1971
Herczog A., Glass Ind., 48 (1967) 445.
Layton М. M. and Herczog A., Glass Technol., 10 (1969) 50
Lungu S. N. and Popescu H. D., Studii si Cercetari di Chimie, Academia
R. P. R., Ill (1955) 225 Maurer R. D., J. Appl. Phys., 33 (1962) 2132
McMillan P. W" Glass-Ceramics, Academic Press, London-New York, 1964
(2ndedn., 1980) Muan A., Osborn E. F., Phase Equilibria among Oxides in
Steelmaking. Addison - Wesley, 1965 Osborn E. F. et a!., Trans. AlME, 200
(1954) 38
Pavlushkin N. М., Principles of Sital Technology (in Russian),
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